MK2 Print quality issue on surfaces normal to Y axis

#1

Hello,
I’m having an issue with my MK2 sometimes having trouble printing vertical walls normal to the Y axis. It can usually print the walls perfectly fine, but sometimes it has some layers offset by about .6mm, like in the attached photo (a print of a shaft collar). The weird part is that I can have perfectly flat walls AND those choppy walls on the same print. For example, the attached photo has the offset layers on those outside bits, but the rest of the print is perfectly vertical. Has anyone seen anything like this?
image
Checked my hardware and it all seems to be fine. No wobbling of the extruder, no play in the y-axis belt, tightened the bearing zipties, and replaced a bearing that had some play. Could this be a software issue rather than a mechanical one?
Thanks for any input.

#2

I think that’s mechanical. Is your Y-axis pulley on really tight? Is the Y belt holder screwed in tight?